ANATOMY:FOREARM

ANATOMY:

FOREARM

•Extension: elbow (functionally, distal humerus) to wrist

•Bones: ulnar connected by interosseus membrane to the radius

•Movements: flexor-pronation and extension-supination

•Compartments: anterior and posterior muscles with bulk proximal while their tendons are distal (operative site)

•Attachments: muscles attached to medial epicondylar ridge act are flexors; muscles attached to lateral epicondylar ridge are extensors

FOREARM

Spiraling gradually over the length of the forearm, the compartments become truly anterior and posterior in position in the distal forearm and wrist

Because neither boundary is crossed by motor nerves, they also provide sites for surgical incision

Innervation: Flexor-pronator muscles (median nerve and ulna nerve except brachioradialis supplied by the radial nerve); extensor-supinator muscles (radial nerve)

FOREARM

Fascia: ends at the joints; therefore, containing fluids and infections and cannot readily spread to other compartments

The anterior compartment is an exception because it communicates with the central compartment of the palm through the carpal tunnel

Muscle: The flexor muscles of the anterior compartment have approximately twice the bulk and strength of the extensor muscles of the posterior compartment

FLEXOR-PRONATOR MUSCLES

The tendons of most flexor muscles are located on the anterior surface of the wrist and are held in place by the palmar carpal ligament and the flexor retinaculum (transverse carpal ligament), thickenings of the antebrachial fascia

Layers: 3- superficial (pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris), intermediate (flexor digitorum superficialis) and deep (flexor digitorum profundus, flexor pollicis longus, and pronator quadratus)

FLEXOR-PRONATOR MUSCLES

The five superficial and intermediate muscles cross the elbow joint; the three deep muscles do not. With the exception of the pronator quadratus

The more distally placed a muscle's distal attachment lies, the more distally and deeply placed is its proximal attachment

The long flexors of the digits (flexor digitorum superficialis and flexor digitorum profundus) also flex the metacarpophalangeal and wrist joint

FLEXOR-PRONATOR MUSCLES

The flexor digitorum profundus flexes the fingers in slow action; this action is reinforced by the flexor digitorum superficialis when speed and flexion against resistance are required.

Tendons of the long flexors of the digits pass through the distal part of the forearm, wrist, and palm and continue to the medial four fingers. The flexor digitorum superficialis flexes the middle phalanges, and the flexor digitorum profundus flexes the distal phalanges.

PRONATOR TERES

It is a fusiform muscle which is the most lateral of the superficial forearm flexors. Its lateral border forms the medial boundary of the cubital fossa.

Test: the person's forearm is flexed at the elbow and pronated from the supine position against resistance provided by the examiner. If acting normally, the muscle is prominent and can be palpated at the medial margin of the cubital fossa.

FLEXOR CARPI RADIALIS

•FCR is a long fusiform muscle located medial to the pronator teres

•Movement: flexion (with the flexor carpi ulnaris), abduction of the wrist (with the extensors carpi radialis longus and brevis), alone,FCR produces a combination of flexion and abduction simultaneously at the wrist so that the hand moves anterolaterally

•The FCR tendon is a good guide to the radial artery, which lies just lateral to it

•Test: the person is asked to flex the wrist against resistance. If acting normally, its tendon can be easily seen and palpated

PALMARIS LONGUS

•Fusiform muscle with a short belly and a long, cord-like tendon that passes superficial to the flexor retinaculum and attaches to it and the apex of the palmar aponeurosis

•It is a useful guide to the median nerve at the wrist; the tendon lies deep and slightly medial to this nerve before it passes deep to the flexor retinaculum.

•Test: the wrist is flexed and the pads of the little finger and thumb are tightly pinched together. If present and acting normally, the tendon can be easily seen and palpated.

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FLEXOR CARPI ULNARIS

•FCU is the most medial of the superficial flexor muscles

•Movement: flexes and adducts the hand at the wrist if acting alone, wrist flexion with FCR and adducts it extensor carpi ulnaris

•The ulnar nerve enters the forearm by passing between the humeral and the ulnar heads of its proximal attachment. It is fully innervated by the ulnar nerve; the tendon of the FCU is a guide to the ulnar nerve and artery, which are on its lateral side at the wrist.

•Test: the person puts the posterior aspect of the forearm and hand on a flat table and is then asked to flex the wrist against resistance while the examiner palpates the muscle and its tendon.

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FLEXOR DIGITORUM SUPERFICIALIS

•FDS is often included with the superficial muscles of the forearm. When considered this way, it is the largest superficial muscle in the forearm. However, it is intermediate. The median nerve and ulnar artery enter the forearm by passing between its humeroulnar and radial heads

•Movement: flexes the middle phalanges of the medial four fingers at the proximal interphalangeal joints, flexes the proximal phalanges at the metacarpophalangeal joints and the wrist joint, it is capable of flexing each finger it serves independently.

•Test: one finger is flexed at the proximal interphalangeal joint against resistance and the other three fingers are held in an extended position to inactivate the flexor digitorum profundus.

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FLEXOR DIGITORUM PROFUNDUS

•FDP is the only muscle that can flex the distal interphalangeal joints of the fingers

•Movement: flexes the distal phalanges of the medial four fingers after the FDS has flexed their middle phalanges (i.e., it curls the fingers and assists with flexion of the hand, making a fist), it can flex only the index finger independently; thus the fingers can be independently flexed at the proximal but not the distal interphalangeal joints.

•Test: the proximal interphalangeal joint is held in the extended position while the person attempts to flex the distal interphalangeal joint. The integrity of the median nerve in the proximal forearm can be tested by performing this test using the index finger, and that of the ulnar nerve can be assessed by using the little finger.

FLEXOR POLLICIS LONGUS

•FPL is lateral to the FDP, where it clothes the anterior aspect of the radius distal to the attachment of the supinator.

•Movement: primarily flexes the distal phalanx of the thumb at the interphalangeal joint and, secondarily, the proximal phalanx and 1st metacarpal at the metacarpophalangeal and carpometacarpal joints, respectively, it is the only muscle that flexes the interphalangeal joint of the thumb. It also may assist in flexion of the wrist joint.

•To test the flexor pollicis longus, the proximal phalanx of the thumb is held and the distal phalanx is flexed against resistance.

PRONATOR QUADRATUS

It is quadrangular and pronates the forearm. It cannot be palpated or observed, except in dissections, because it is the deepest muscle in the anterior aspect of the forearm.

Movement: it is the prime mover for pronation. The muscle initiates pronation; it is assisted by the pronator teres when more speed and power are needed. The pronator quadratus also helps the interosseous membrane hold the radius and ulna together, particularly when upward thrusts are transmitted through the wrist (e.g., during a fall on the hand).

EXTENSOR MUSCLES

•Groups: 3- Muscles that extend and abduct or adduct the hand at the wrist joint (extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris), Muscles that extend the medial four fingers (extensor digitorum, extensor indicis, and extensor digiti minimi), Muscles that extend or abduct the thumb (abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus).

•The extensor tendons are held in place in the wrist region by the extensor retinaculum, which prevents bowstringing of the tendons when the hand is extended at the wrist joint. As the tendons pass over the dorsum of the wrist, they are provided with synovial tendon sheaths that reduce friction for the extensor tendons as they traverse the osseofibrous tunnels formed by the attachment of the extensor retinaculum to the distal radius and ulna

EXTENSOR MUSCLES

•Anatomical layers: superficial and deep. Four of the superficial extensors (extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris) are attached proximally by a common extensor tendon to the lateral epicondyle

•The proximal attachment of the other two muscles in the superficial group (brachioradialis and extensor carpi radialis longus) is to the lateral supraepicondylar ridge of the humerus and adjacent lateral intermuscular septum. The four flat tendons of the extensor digitorum pass deep to the extensor retinaculum to the medial four fingers. The common tendons of the index and little fingers are joined on their medial sides near the knuckles by the respective tendons of the extensor indicis and extensor digiti minimi (extensors of the index and little fingers, respectively).

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BRACHIORADIALIS

Fusiform muscle, lying superficially on the anterolateral surface of the forearm; forms the lateral border of the cubital fossa. It flexes the forearm at the elbow. It is especially active during quick movements or in the presence of resistance during flexion of the forearm.

 The brachioradialis and the supinator are the only muscles of the compartment that do not cross and therefore are incapable of acting at the wrist. As it descends, the brachioradialis overlies the radial nerve and artery where they lie together on the supinator, pronator teres tendon, FDS, and FPL. The distal part of the tendon is covered by the abductors pollicis longus and brevis as they pass to the thumb.

Test: the elbow joint is flexed against resistance with the forearm in the midprone position. If the brachioradialis is acting normally, the muscle can be seen and palpated.

EXTENSOR CARPI RADIALIS LONGUS

ECRL is a fusiform muscle overlapped by the brachioradialis, with which it often blends. As it passes distally, posterior to the brachioradialis, its tendon is crossed by the abductor pollicis brevis and extensor pollicis brevis. The ECRL is indispensable when clenching the fist

Test the wrist is extended and abducted with the forearm pronated. If acting normally, the muscle can be palpated inferoposterior to the lateral side of the elbow. Its tendon can be palpated proximal to the wrist

EXTENSOR CARPI RADIALIS BREVIS

ECRB and ECRL pass under the extensor retinaculum together within the tendinous sheath of the extensor carpi radiales

When the two muscles act by themselves, they abduct the hand as they extend it. Acting with the extensor carpi ulnaris, they extend the; acting with the FCR they produce pure abduction. Their synergistic action with the extensor carpi ulnaris is important in steadying the wrist during tight flexion of the medial four fingers (clenching a fist), a function in which the longus is more active

EXTENSOR DIGITORUM

It is the principal extensor of the medial four fingers occupying much of the posterior surface of the forearm. Normally no finger can remain fully flexed as the other ones are fully extended. Commonly, the fourth tendon is fused initially with the tendon to the ring finger and reaches the little finger by a tendinous band.

Test: the forearm is pronated and the fingers are extended. The person attempts to keep the fingers extended at the metacarpophalangeal joints as the examiner exerts pressure on the proximal phalanges by attempting to flex them. If acting normally, the extensor digitorum can be palpated in the forearm, and its tendons can be seen and palpated on the dorsum of the hand.

EXTENSOR DIGITI MINIMI

EDM, a fusiform slip of muscle, is a partially detached part of the extensor digitorum. The tendon of this extensor of the little finger runs through a separate compartment of the extensor retinaculum, posterior to the distal radioulnar joint, within the tendinous sheath of the extensor digiti minimi. The tendon then divides into two slips; the lateral one is joined to the tendon of the extensor digitorum, with all three tendons attaching to the dorsal digital expansion of the little finger. After exerting its traction primarily on the 5th finger, it contributes to extension of the hand.

EXTENSOR CARPI ULNARIS

ECU, a long fusiform muscle medially located, has 2 heads: a humeral head and an ulnar head

Acting with the ECRL and ECRB, it extends the hand; acting with the FCU, it adducts the hand. Like the ECRL, it is indispensable when clenching the fist.

Test: the forearm is pronated and the fingers are extended. The extended wrist is then adducted against resistance. If acting normally, the muscle can be seen and palpated in the proximal part of the forearm and its tendon can be felt proximal to the head of the ulna.

SUPINATOR

It lies deep in the cubital fossa and, along with the brachialis, forms its floor

The deep branch of the radial nerve passes between the humeral and ulnar heads as it leaves the cubital fossa to enter the posterior part of the arm thereby forming the posterior interosseus nerve. The supinator rotates the radius

The deep extensors of the forearm act on the thumb and the index finger (extensor indicis). The three muscles acting on the thumb are referred to as outcropping muscles

ABDUCTOR POLLICIS LONGUS

APL is fusiform and lies just distal to the supinator and is closely related to the EPB

It acts with the APB during abduction of the thumb and with the extensor pollicis muscles during extension of this digit

Test: the thumb is abducted against resistance at the metacarpophalangeal joint. If acting normally, the tendon of the muscle can be seen and palpated at the lateral side of the anatomical snuff box and on the lateral side of the adjacent extensor pollicis brevis tendon.

EXTENSOR POLLICIS BREVIS

In continued action after acting to flex the proximal phalanx of the thumb, or acting when that joint is fixed by its antagonists, it helps extend the 1st metacarpal and extend and abduct the hand. When the thumb is fully extended, a hollow called the anatomical snuff box, can be seen on the radial aspect of the wrist

Test: the thumb is extended against resistance at the metacarpophalangeal joint. If the EPB is acting normally, the tendon of the muscle can be seen and palpated at the lateral side of the anatomical snuff box and on the medial side of the adjacent APL tendon

EXTENSOR POLLICIS LONGUS

The tendon passes under the extensor retinaculum in its own tunnel, within the tendinous sheath of the extensor pollicis longus, medial to the dorsal tubercle of the radius. It uses the tubercle as a trochlea (pulley) to change its line of pull as it proceeds to the base of the distal phalanx of the thumb. The gap thus created between the long extensor tendons of the thumb is the anatomical snuff box. The EPL also adducts the extended thumb and rotates it laterally.

EXTENSOR POLLICIS LONGUS

To test the extensor pollicis longus, the thumb is extended against resistance at the interphalangeal joint. If the EPL is acting normally, the tendon of the muscle can be seen and palpated on the medial side of the anatomical snuff box.

The tendons of the APL and EPB bound the anatomical snuff box anteriorly, and the tendon of the EPL bounds it posteriorly. The snuff box is visible when the thumb is fully extended; this draws the tendons up and produces a triangular hollow between them. Observe that the:

Radial artery lies in the floor of the snuff box.

Radial styloid process can be palpated proximally and the base of the 1st metacarpal can be palpated distally in the snuff box.

EXTENSOR INDICIS

The extensor indicis has a narrow, elongated belly that lies medial to and alongside that of the EPL. This muscle confers independence to the index finger in that the extensor indicis may act alone or together with the extensor digitorum to extend the index finger at the proximal interphalangeal joint, as in pointing. It also helps extend the hand.

ARTERIES OF THE FOREARM

VEINS OF THE FOREARM

NERVES OF THE FOREARM

NEUROVASCULAR STRUCTURES OF THE FOREARM

CLINICAL ANATOMY

Elbow Tendinitis or Lateral Epicondylitis

Mallet or Baseball Finger

Fracture of the Olecranon

Synovial Cyst of the Wrist

Median Nerve Injury

Pronator syndrome

Ulnar and radial Nerve Injury

SURFACE ANATOMY